The role of uranium peroxide studtite on the retention of Cs, Sr and Se(VI)

Abstract

The formation of uranyl secondary solid phases onto the spent nuclear fuel surface might influence the radionuclide concentration in solution via, among others, sorption processes. In this work, the incorporation of some radionuclides onto the uranium peroxide studtite, UO 2 O 2 ·4H 2 O, has been tested.The study was carried out in batch experiments where a known amount of studtite (0.05 g) was put in contact with 20 cm 3 of radionuclide solution. Once equilibrium was reached, radionuclide concentrations in solution were determined by ICP-MS. The radionuclide amount attached to the solid was calculated from the mass balance. The S/V values of the experiments were also determined from BET specific solid surface area measurements.In this work, data on sorption of caesium, strontium, and selenium as a function of pH are presented. The behaviour of caesium and strontium are similar: a relatively high amount of radionuclide is sorbed at neutral to alkaline pH while there is almost no sorption at acidic pH. On the other hand, in the case of selenium, the sorption maximum occurs at acidic pH and there is almost no sorption at alkaline pH. The different behavior of the radionuclides is related to the element speciation in solution and the surface charge of the solid. Strontium and caesium are sorbed at alkaline pH because they are positively charged in solution and the surface of the studtite is negatively charged (>Ogroups) while selenium(VI) sorbs at acidic pH because the surface of the studtite is positively charged, and the predominant selenium(VI) species in solution is anionic.These preliminary data indicate that the sorption capacity of uranyl secondary solid phases such as studtite is an important process to be considered when establishing the migration of different radionuclides released from spent nuclear fuel.

Retention of cesium and strontium by uranophane, Ca(UO2)2(SiO3OH)2·5H2O

“…Cesium and strontium solutions were prepared dissolving CsClO 4 (Acros Organics) and Sr(NO 3 ) 2 (Merck) in Milli-Q water. Sorption batch experiments were carried out at room temperature and following the same methodology reported in previous works (see for example reference [19]). In short, 0.05 g of uranophane were put in contact with 20 cm 3 of a strontium or cesium solution in polystyrene tubes.…”

Study of near field processes involved in the oxidative dissolution of the spent nuclear fuel and radionuclides release

“…As it was observed in a previous chapter, Cs is one of the most mobile RN inside the SNF and it is expected to be partially segregated in the gap and GB. As it was mentioned before, 135 Cs (half-life: 3•10 6 years) and 137 Cs (half-life: 30 years) are long lived isotopes and therefore, a special effort has been done to determine possible retention of this specific element (Douglas et al, 2002;Gimenez et al, 2009;. (Rovira et al, 2003).…”

“…Even though 90 Sr isotope is short-lived (half-life: 28.8 years), it is of interest due to the substitution of Ca 2+ by Sr 2+ in some structures such as human bone structure. As a consequence, the retention of Sr under relevant conditions for the DGR has been also studied (Douglas et al, 2002;Gimenez et al, 2009;Sureda et al, 2010).…”